There were originally two wooden chapels in Kustavi, one in Vartsala (first record from the year 1554) and another in Kunnarainen (1675). In 1783 Kunnarainen chapel was moved to the current site and reconstructed by J. Höckert. The new parish church was named after the king of Sweden, Gustaf III. The church was enhanced between years 1876-1879 and again in 1928.
The pulpit dates back to the 1640s. There are also couple of beautiful miniature ships (so-called votive ships) made by local islanders. The church environment is a well-preversed sample of wooden architecture in Finland.
Towering 52 meters above the sea, Bengtskär lighthouse is the tallest one in Scandinavia. The building started in in 1905 after the shipwreck of S/S Helsingfors and was completed in 1906. The lighthouse was designed by architect Florentin Granholm. On December a special petrol lantern, designed and built in Paris, was brought to Bengtskär and installed atop the tower.
German fleet bombarded Bengstkär in the First World War in 1914. Since the Gulf of Finland was heavily mined, it was not until 1919 that the surrounding seas were declared safe for shipping, that the light was lit again.
After the war the military value of Bengtskär increased as part of the defence system of independent Finland. In Second World War (1941) Soviet Union made a suprise attack to island. After a bloody battle, the small Finnish garrison emerged victorious. Intermittent repairs to the facility continued during the post-war period.